Differences in the tumor necrosis factor-alpha-mediated lysis by fixed natural cytotoxic cells and fixed cytotoxic macrophages.

TNF-alpha has been shown to be associated with macrophage cell membranes in such a way as to retain cytolytic activity despite fixation of the macrophage effector cells with paraformaldehyde. In this paper we report that, similar to cytotoxic macrophages, natural cytotoxic (NC) cells also use cell-associated TNF to lyse sensitive target cells. However, in contrast to fixed cytotoxic macrophages, NC cells do not retain cytolytic activity after fixation with paraformaldehyde. Additionally, the cytolytic activity of paraformaldehyde-fixed NC cells is not increased by incubation with LPS or by incubation with rTNF before fixation. Western blot analysis indicates that, unlike macrophages, NC cells use a smaller (17 kDa) constitutively active form of TNF. These results indicate that, although both macrophages and NC cells use effector cell-associated TNF to mediate lysis of sensitive targets, the way in which TNF is associated with these two types of effector cells must be different.